1. Field of the Invention
The invention is related to the production of corrugated cardboard.
2. Brief Description of the Background Art
The invention relates to a device for production of corrugated cardboard comprising:
a) a first fluted roller and a second fluted roller, which together make a corrugated deforming gap; PA1 b) a pressure contact roller, which together with the second fluted roller makes a pressure contact group; PA1 c) a feeding means to feed a strip to be corrugated to the corrugated deforming gap, in which the strip to be corrugated is formed into a corrugated strip; and PA1 d) a feeding means to feed a smooth strip to the pressure contact gap, in which the smooth strip is pressed into contact with the corrugated strip, with an intermediate glue layer, and advancing means to advance the composite strip produced by bonding the corrugated strip and the smooth strip, wherein
each of the two fluted rollers has a fluted profile on its periphery with peaks and valleys extending in the respective axial direction and cooperating in the corrugated deformation, successive profile peaks and valleys of each fluted roller being defined by profile flanks, and the profile peaks of each fluted roller having a sharper curvature than the profile valley of the respective other fluted roller corrugatingly cooperating with them.
Devices of this kind are built with fluted rollers of different shapes, the profile being determined by the pitch (i.e., the distance between successive teeth) and tooth height. In the process of production, the paper strip is compressed under pressure and heat between the profiles of the meshing fluted rollers and then bonded to a smooth covering strip. This too, as a rule, is done under the action of heat and pressure by means of a so-called pressure contact roller or press roller.
The actual corrugation forming process takes place between the respective fluting or profile peaks of the one fluted roller and the bottom of the flutings, or the profile valleys, of the other fluted roller. The flank as a rule does not participate. In these designs, the difference between the radii of cooperating profile peaks and valleys is critical.
In conventional corrugating devices, the profiles of the two fluted rollers are identical, so that the corrugation of the paper is the same in both directions of flexure, and a symmetric profile of the finished corrugated paperboard results.
In the region of contact between the second fluted roller and the pressure contact roller, contact between the profile peaks of the second fluted roller and the essentially cylindrical surface of the pressure contact roller takes place. As a result of this, the axial distance between these two rollers, defined by the contact between the second fluted roller and the pressure contact roller, varies continually in the course of rotation of the rollers between a maximum value, when a profile peak is located in the region of a plane containing the centerlines of the rollers, and a minimum distance, when a profile valley of the second fluted roller is located in the connecting plane containing the centerlines of the rollers. This distance variation leads to a continual excitation of vibrations, the amplitude of vibration that occur resulting in surface marking of the pressure contact roller side of the smooth strip and, especially in intervals of resonance, possible damage to the paper fibers in the pressure contact gap. The wider the pitch of the fluted profile, the greater the damaging amplitude of vibration may become. To solve this problem, one might consider working with lower pressures and longer exposure time between the second fluted roller and the pressure contact roller. Providing a longer exposure time would be needed to establish intimate connection between the corrugated strip and the smooth strip.